With an increasing concern over the pollution in the atmosphere, there is a great burden placed on industry to produce environmentally safe products and to do so in an environmentally safe manner. An area that has been of particular concern is the release of sulfur and sulfur compounds into the atmosphere during the refining of petroleum, the sweetening of natural gas, the processing of ore, the destructive distillation of coal, and other processes which produce sulfur containing gases.
The presence of significant quantities of hydrogen sulfide (H2S) and carbon dioxide (CO2) in various xe2x80x9csourxe2x80x9d industrial gaseous streams poses a persistent problem. Although there are various procedures that have been developed to remove and recover these contaminants, these procedures are deficient in some way or another. For example, one process that has been developed utilizes aqueous alkaline solutions to absorb H2S from a gas stream and to convert the absorbed H2S to elementary. sulfur. Generally, this type of a process utilizes an aqueous alkaline solution containing vanadium ions and anthraquinone disulfonate, i.e., acid (ADA). This particular type of process, however, only works with dilute aqueous solutions and low H2S loading. A dilute aqueous solution is required because when higher concentrations are used, sufficient levels of vanadium that oxidize the sulfur compounds can not be maintained in solution. Low concentrations, however, result in high circulation rates, large capital investments, and higher production costs. In addition, a dilute aqueous alkaline solution is not capable of CO2 removal.
Another problem associated with these processes is the breakdown and disposal of the ADA, an additive used in this type of process. The breakdown and disposal of this compound and compounds similar to it is difficult and expensive. Thus, adding ADA and/or ADA-like compounds actually increase the cost associated with this type of process.
Accordingly, there is a need for an improved process to control the removal of H2S and C02 from various xe2x80x9csourxe2x80x9d gases in an economical and environmentally safe way. The improved process should be capable of removing H2S and CO2 with solutions having adequate H2S loads without using harmful additives like ADA or ADA-like compounds. The present invention is directed to such an improved process.
The present invention relates to a process for the removal of minor sulfur compoundsxe2x80x94mainly H2S and CO2 from a gaseous mixture that contains the same. Examples of a gaseous mixture include natural gas, iron ore reduction gas, etc. The process contacts a sour gas mixture with an aqueous alkaline solution comprising an oxidizing agent in a 10 to 1 molar ratio of an oxidizing agent to H2S gas. The oxidizing agent is contacted with the gaseous mixture at a temperature of about 150 degrees F. to about 300 degrees F. so that the gaseous mixture is absorbed into the aqueous alkaline solution.
Once absorbed, H2S is oxidized by vanadium ions present in the aqueous alkaline solution into elementary sulfur. The elementary sulfur is removed from the aqueous mixture to produce an aqueous alkaline solution having less sulfur than the initial gaseous mixture absorbed into the aqueous alkaline solution. After H2S is removed from the aqueous alkaline solution as elementary sulfur, CO2 is stripped from the aqueous alkaline solution to produce an aqueous alkaline solution containing less H2S and less CO2 than the initial gaseous mixture absorbed into the aqueous alkaline solution.
The aqueous alkaline solution used in the process described above comprises about 15% to about 40% by weight of K2CO3, up to about 10% by weight of V2O5, and up to about 10% by weight of equivalent H3BO3 The pH of the aqueous alkaline solution is buffered at a pH below 10 and the pressure is maintained above atmospheric pressure. The pressure and temperature ranges maintained keep a more concentrated alkaline solution and, therefore, help to maintain the tetravalent vanadium ions from V2O5, above 65% of the total vanadium ions in the aqueous solution. This high percentage of tetravalent vanadium ions facilitates regeneration of spent V+5 and, thus complete oxidization of the sulfur compounds in the aqueous gaseous mixture without the use of additives like ADA and/or ADA-like compounds.